In the innervated and vascularly isolated carotid sinus, infusion of 5 micrograms/ml of propranolol enhances carotid sinus nerve activity. Superfusion at constant pressure or flow indicates that this is due to a decrease in sinus wall elasticity which may increase the load upon the series-arranged baroreceptors. Chronic studies in this grant period will be designed to record neurophysiological activity from the effector and receptor limb of the baroreceptor depressor reflex arc. Cats will receive propranolol for a period of one month and sinus nerve activity at differing pressures compared with acute administration of the drug. Evidence that the superior cervical ganglion may contribute a significant input to the carotid sinus provides a mechanism whereby propranolol effects distensibility. In spontaneous hypertensive rats (SHR), the relationship of hypertension, propranolol and sympathetic innervation to the efficacy of the drugs action and to the initial hypertensive condition will be investigated by selective bilateral denervation of the superior cervical ganglion.